RAMJobStore.RemoveCalendar fails when triggers are present. The reason is that foreach is mistakenly iterated through Trigger, not TriggerWrapper, 'trigger' collection. The correct code is

foreach (TriggerWrapper tw in triggers)
{
 if (tw.Trigger.CalendarName != null &&
    tw.Trigger.CalendarName.Equals (calName))
       {
         numRefs++;
       }
}